Here are the correct answers with explanations for each question:

**11. The boss allows __________ home.**
**C. us staying**
**Explanation:** The construction "allows us to stay" is grammatically correct, but the sentence suggests "allows us staying" as a more informal way of saying it, which is more acceptable in conversational English.

**12. Organic farming is better for the environment, __________ it doesn't use harmful chemicals.**
**D. but**
**Explanation:** "But" is the correct conjunction that introduces a contrasting idea, since the second part of the sentence presents an alternative explanation.

**13. They have already decided on their next summer holiday. They __________ do a tour of the country.**
**A. are going to**
**Explanation:** "Are going to" indicates a planned action in the future, which is appropriate here since the decision has already been made.

**14. I think the final match _______________ very exciting.**
**A. will be**
**Explanation:** "Will be" correctly indicates a future prediction about the match.

**15. Her first novel _______________ into English last year.**
**B. was translated**
**Explanation:** "Was translated" is the correct past passive form, indicating that the action happened last year.

**16. Plants in the garden _________ by my father every day.**
**C. are watered**
**Explanation:** "Are watered" is the correct present passive form indicating a habitual action.

**17. A wildlife documentary _____________ on TV tonight.**
**C. will be shown**
**Explanation:** "Will be shown" indicates a future event and is appropriately used for a scheduled program.

**18. They decided ___________ to the live concert.**
**A. to go**
**Explanation:** "To go" is the correct infinitive form that follows the verb "decided."

**19. I saw her ___________ the street.**
**A. cross**
**Explanation:** "Cross" is the correct base form of the verb used after "saw" to indicate a completed action.

**20. I heard someone ______________ the window last night.**
**B. open**
**Explanation:** "Open" is the correct base form of the verb used after "heard" to indicate a completed action.

### Summary of Answers:
11. C
12. D
13. A
14. A
15. B
16. C
17. C
18. A
19. A
20. B